The invention relates to a colour cathode ray tube system comprising a colour cathode ray tube comprising an electron gun for generating at least one electron beam, a colour selection electrode having rows of apertures, a display screen and means for deflecting the electron beam across the colour selection electrode in a line deflection direction transverse to the row of apertures.
Such display devices are known. They are used, inter alia, in television receivers.
A disturbing effect which may occur in such display devices is the so-called Moire effect. This effect causes light and dark lines or lines of a deviating colour in the image.
In operation, lines are written on the display screen in the line deflection direction by the electron beam(s). The number of lines written on the display screen (the so-called number of active lines) is system-dependent. In the PAL and SECAM systems approximately 537 lines are written on the display screen, (in these systems the signal comprises 625 lines; approximately 50 of said lines are used for coded information; of the remaining 575 lines approximately 7% is scanned beside the display screen, the so-called "overscan"; thus, the overall number of active lines is approximately (625-50)/1.07=537). In the NTSC system approximately 452 active lines are written (the NTSC signal comprises 525 lines). In operation, a colour cathode ray tube preferably does not exhibit disturbing Moire effects.